Capture

Then there is the excitement of the shot itself.  When a great original scene presents itself, maybe fleetingly, your heart will pound, but it must be stilled.  You may have only one chance to get this photo.

That being the case, my advice is to take a shot right away with whatever settings are on your camera or set it to auto and shoot.  Worry about the problems in post-capture, but at least you have the shot. 

If the light is still good, take a deep breath and slow down. Under no circumstances should you repeat the shot you just took. Think about the composition of the shot.  Take care to get the focus point of your camera exactly where you want it.  Are the shutter, aperture and ISO settings what this shot needs?  The light may be dim.  You may need a slow shutter speed.  Yes, your camera has great stabilization, but you may need more.  Is there something solid you can lean your back against?  Is there something to rest the camera on? A really solid position is to sit down with your back against something sturdy and both knees bent up in front of you.   If none of that is possible, put one leg forward, one leg back.  Rest firmly on your back leg and steady your body, elbows against the chest.  Take a deep breath. If you can do it, listen carefully to your heartbeat.  When you are ready to shoot, hold your breath; and press the shutter smoothly and carefully. 

If there is time for another, reconsider everything.  Would another angle be better?  Should you go for a wide angle or a telephoto? If there is a lot of contrast, consider exposure bracketing. Should you use high dynamic range? What about focus stacking?

This is your shot.  If the time is fleeting, there is no point in wasting it with haste. Slow down.  You will be rewarded for doing so.